In recent years, there has been an exponential increase in demand for wireless communications services, which was initiated by the development of cellular telephones. Cellular telephones permit subscribers to initiate telephone calls to other mobile subscribers or fixed stations in the Public Switched Telephone Network (PSTN), or to receive calls from either of those sources. Typically, communications between a subscriber using a wireless transceiver and a called station, is mediated by a Mobile Switch Center (MSC), which functions as a Service Switching Point (SSP) in the PSTN. MSCs control wireless communications with each wireless transceiver operating within a service area covered by the MSC. In order to provide wireless communication services over a large geographic area, it is common to divide the coverage area of the wireless network into discrete service areas (cells) several of which are collectively served by a respective MSC. MSCs operated by a wireless communications service provider are commonly interconnected by time division multiplexed (TDM) trunk facilities. Each subscriber of wireless telecommunications services is assigned a telephone number by the service provider associated with one of the MSCs. That MSC serves as a home MSC for the subscriber. The address (telephone number) of the subscriber's wireless transceiver is recorded in a home location register (HLR) maintained by the home MSC. Calls directed to the subscriber's address are routed using translation tables in the PSTN to the home MSC.
In order to enhance mobility of the subscriber, the HLR also contains information identifying a current location of the subscriber's wireless transceiver. As the subscriber roams from one cell to another, control of wireless communications with the wireless transceiver is transferred to the MSC serving the cell within which the wireless transceiver is located. The address of the “current MSC” is recorded in the HLR maintained by the home MSC of the wireless transceiver as the current location of the wireless transceiver. With this arrangement, an inbound call destined for a subscriber's wireless transceiver is automatically routed to the home MSC. Upon receipt of the call set-up messages, the home MSC queries its HLR to obtain the current location of the wireless transceiver, and then routes the inbound call to the current MSC, if it is different from the home MSC, in order to complete the call.
This conventional arrangement has a disadvantage in that, as the number of subscribers increases, substantial resources of each MSC become tied-up routing inbound calls to other MSCs to serve roaming subscribers. Additionally, as the number of MSCs increases, the size and complexity of the trunk facilities required to handle the inter-MSC traffic also increases.
In order to address these issues, it is known to designate one of the MSCs as a “Gateway MSC”, and route all inbound calls to wireless subscribers through the Gateway MSC. The Gateway MSC uses the call set-up messages for the inbound call to identify the home MSC, and queries the HLR maintained by the home MSC to obtain the current location of the called wireless transceiver. The Gateway MSC can then route the inbound call to the current MSC, bypassing the home MSC if the subscriber is roaming, so that the inbound call can be completed without requiring resources of the home MSC. This solution helps to reduce congestion in the mobile network. However, it also tends to increase the size and complexity of the interoffice trunking network because each MSC must be connected to a Gateway MSC in addition to being interconnected with the other MSCs. In addition, since all inbound traffic is routed through the Gateway MSC, congestion of trunks associated with the Gateway MSC is also increased as demand for wireless communications services grows.
Co-pending and co-assigned U.S. patent application Ser. No. 09/158,855, filed Sep. 23, 1998 and entitled TRANSIT TRUNK SUBNETWORK SYSTEM teaches the connection of SSPs to a broadband packet network (e.g. an Asynchronous Transfer Mode (ATM) or Internet Protocol (IP) backbone) which provides dynamic trunking between the SSPs over Switched Virtual Circuits (SVCs) set up through the broadband packet network. The application also teaches that the broadband packet network can be used for trunking between MSCs of a wireless network, thus providing a means of dramatically simplifying inter-MSC trunking by replacing interoffice TDM trunks with broadband packet network facilities. However, this solution relies on a Gateway MSC through which inbound calls are routed in order to enable identification of home MSCs and querying of the associated HLRs to determine a current location of called wireless subscribers. The Gateway MSC therefore becomes a bottleneck to traffic handling as the number of mobile subscribers increases. Alternatively, the Gateway MSC functionality may be distributed among the MSCs in the wireless network. However, this solution has a disadvantage in that the Gateway MSC functionality must be installed and maintained in each of the distributed Gateway MSCs. This contributes to operating overhead and capital expense.
Accordingly, there exists a need for a low cost and highly scalable means for enabling communications between wireline and wireless subscribers.